Apparatus and method for silk screen or screen printing around the edge of an object of a rigid material

Abstract: The apparatus for screen printing from one edge to the other of an object in a rigid material, beside the conventional components for screen printing, includes second ink scraping means (8), acting on the lower face of the printing frame (3), for removing ink from the portion of design (5) that exceeds the perimetric dimensions of the object (6) to be printed. Through said apparatus it is possible to perform a method for screen printing from one edge to the other of an object made of a rigid material, which method consists of printing the design on the object, exceeding the printing on at least one of the edges of the object; spacing the printing frame from the printed object and scraping, from the lower face of the printing frame facing the object, ink which has not been deposited on the object because of the lesser dimensions of the object with respect of the design.

Description: The present invention relates to an apparatus and a method for silk-screen, or screen, printing from one edge to the other of an object in a rigid material. As known, when screen printing on an object made of a rigid material several variables have to be taken into account, otherwise the quality of the printing is low. For example, when screen printing on an object it is always necessary to check the standard parameters of the screen printing process such as the fabric tension, the compensation of the image deformation, the pressure, stiffness and inclination of the doctor blade and, not least important, the dimensional variation of the film or of the frame due to the variations of the work conditions. There are even more difficulties in obtaining a good quality screen printing when, as it normally happen, the object to be printed is mass produced and its real dimensions, with respect to the nominal designed dimensions, vary from the first piece to the last one produced. The above problems in printing across the edges of an object, are conventionally solved in a very simple way. The design to be printed on the object is realized on the printing frame or screen, and is uniformly shrank for a selected value (one millimeter or more) with respect of the real perimetric dimensions of the object. In this manner, it is mathematically assured to always print correctly, regardless of the dimensional variations of the object due to the inability to maintain the working tolerances in mass productions, or regardless of the standard parameters used in screen printing. In other words, after centering the object on the frame, since the design is smaller than the object, its final result is always assured. The only inconvenience of this printing method is that the printed object has an unprinted small area around the edges. For example, if the rigid object to be printed is a vehicle window pane, the peripheral black print (almost all the car manufacturers adopt this solution) because of the above reasons will not reach the edges of the pane and a peripheral strip will remain unprinted. Recently, however, in the new automatic systems for assembling the window panes on the vehicles, the pane edges are left exposed and therefore the panes have to be printed from one edge to the other without discontinuity. For the above reasons, the screen printing on windshields, door windows, rear windows, overhead windows, etc., is performed twice across two edges each time. It is easily understood however that with this solution there is an area of the pane, or object, with a double printing and therefore with a product of lower quality. Furthermore, if all the edges of the object have to be printed, it is necessary to reposition the object on the printing bed with a considerable waste of time. It is also noted that after printing two edges it is necessary to wait for the object to dry before printing the other two edges, causing a further waste of time and rendering this method extremely costly. Therefore, this solution does not guarantee a precise and accurate printing and even considerably increases the cost of each produced unity. The aim of the present invention is to eliminate the above drawbacks of the prior art by devising an apparatus and a method, for screen printing from one edge to the other of an object in rigid material, without any discontinuity, even when the external dimensions of the object to be printed have a negative or positive variation with respect to the nominal dimensions and regardless of the standard parameters used in screen printing such as the fabric tension, the compensation of the image deformation, the pressure, stiffness and inclination of the doctor blade, the dimensional variations of the film or of the frame due to the working conditions. Within this aim, an important object of the invention is to devise an apparatus and a method for screen printing from one edge to the other of a rigid material which does not require to print only across two edges at a time, with consequent waste of time, allowing instead to reduce the cost of each produced item and reducing the start up costs. In US-A-4 389 936 is disclosed an apparatus for over the edge printing as defined in the pre-characterizing part of claim 1. Said apparatus does not provide a scraper acting on the lower face of the printing frame and means, for removing the ink from said scraper, wich move along a path orthogonal to the path followed by said scraper. A further object of the invention is to devise an apparatus and a method for screen printing from one edge to the other of an object in rigid material, which can be used for any type of object to be printed, independently of the object dimensions, or of the centering and feeding systems on the printing bed. Not least object of the invention is to devise an apparatus and a method for screen printing from one edge to the other of an object in rigid material which is obviously not limited to car window panes but rather allows to print across two edges, without discontinuity, of contoured objects or squared objects such as shower booths, oven doors, furniture glass panes, etc. The above aim and objects are achieved by an apparatus for screen printing from one edge to the other of an object in rigid material as claimed in the characterizing part of claim 1. Said apparatus allows to perform a method for screen printing from one edge to the other of an object in rigid material, as claimed in the characterizing part of claim 9. Further characteristics and advantages of the invention will be more apparent by the description of a preferred but not exclusive embodiment of an apparatus and a method for screen printing from one edge to the other of an object in rigid material, illustrated, by way of indicative but not exclusive example in the enclosed drawings wherein: Fig. 1 is a schematic bottom plan view of the printing frame having the design to be printed, by screen printing, on a vehicle window pane, shown above, where perimetrically the broken line represents the portion of design exceeding the dimensions of the pane itself; Fig. 2 is a schematic front elevated view of the arrangement of the second scraping means acting on the lower face of the printing frame according to the invention; Figs. 3 and 4 show the different possible movements and embodiments of the second scraping means according to the invention; Fig. 5 is a schematic lateral elevated partial view of the second scraping means arranged below the printing frame; Fig. 6 schematically shows a plan view of the printing bed of the apparatus and of the centering templates of, for example, a vehicle window pane, according to the invention; Fig. 7 is a section view according to the line VII-VII of Fig. 6, showing the cleaning means which can be applied to the sides of the printing bed, according to the invention, for cleaning the pane centering templates; Fig. 8 is a schematic front elevated view of first cleaning means of the lower face of the printing frame, according to the invention; Fig. 9 is an enlarged schematic lateral elevated view of the roll made of absorbent material and of the collecting tray for the ink pressed from the roll, according to the invention; Fig. 10 is an elevated front view of the tray, shown in Fig. 9, supporting the presser members, according to the invention; and Fig. 11 is an enlarged front view exemplifying the absorbent rolls acting on the scrapers according to the invention. With reference to the figures, the apparatus for screen printing from one edge to the other of a rigid material, according to the invention, comprises a printing bed 2 and a printing frame 3 associated therewith in a per se known manner. The printing frame 3 supports a design 5 to be printed, by screen printing, on an object made of rigid material, such as, for example, a car window pane 6. The printing frame, in a per se known manner, also comprises a means for distributing the ink on the frame, a means for pressing the ink through the design 5 and at least a first scraping means of said ink from the printing frame, partially visible in Fig. 5, and generally designated by 7. The apparatus also comprises second scraping means comprising at least one scraper 8, acting on the lower face of the printing frame, i.e. on the face facing the pane 6, advantageously allowing the ink to be removed from the pane and in particular from the portion of the printed design exceeding the peripheral dimensions of the pane 6. More in detail, the scraper 8 moves along a path parallel to and below the path followed by the first scraping means, by the distributing means and by the pressing means, the path comprises a collecting area 9 of the ink which is scraped from below the printing frame. Furthermore, for optimizing the scraping operation, below the printing frame, the axis of the scraping member 10 of the scraper 8, is inclined in order to form an angle equal or less than 90° with the plane of the printing frame on the direction of motion. For example, in Fig. 2, the scraper 8 is shown in a starting position by a broken line and in an end position by a full line, on the right hand side of Fig. 2. As an example, the scraper 8 is shown as providing a partial rotation of its scraping member 10, according to the direction of motion of the scraper, in order to provide the optimal scraping angle, according to the requirements. Furthermore, instead of just one scraper, which would imply an idle stroke of the scraper to return to the starting position, of course it is possible, as illustrated in Figs. 3 and 4, to use two scrapers. In this case, the scraper member 10 of each scraper has a counterposed inclination in order that one scraper or the other may work depending on the direction of scraping, thereby reducing the time required for the scraping operation. Conveniently, instead of the collecting area 9 for the ink scraped from below the printing frame, removing means for removing the ink from the two scraping members 10 are provided outside the printing frame. In particular, for each scraper 8, the removing means comprises a roll 20 made of absorbent material, for example sponge, which is in contact with the scraper member, the roll rotating around its axis and at the same time moving parallel to the longitudinal axis of the scraper. In this manner the roll 20 removes and absorbs the ink from the scraper. Subsequently, when the roll 20 has moved outside the printing frame (Fig. 9) a moving means 22 raises a tray 21 in order to put a presser member, for example a presser roll 23, against the roll 20 in order to press out the ink contained in the roll 20 and collect the ink in the tray 21. Furthermore, first cleaning means of the lower face are provided, in order to prevent any ink leftover from staining the lower face of the printing frame, with all the consequent inconveniences, during the motion of one of the scrapers. The cleaning means comprises a first feed roll 24 for feeding absorbent paper 25 to a second motorized roll 26 for winding the paper. A pusher 27 is provided between the first and second rolls. The pusher is vertically moving with respect to the printing frame and is adapted to guide the paper in contact with the lower face of the printing frame, by means of a plurality of holes 28 arranged on the surface of the pusher for sucking air. In the case of the example illustrated in Fig. 6, where the glass pane is centered on the printing bed by means of templates 12, which remain in the holding position of the pane for the duration of the printing process, since the printed image is larger of the object to be printed, it may happen that some ink stains the templates and this ink has to be removed before the successive printing operation. In this case, the apparatus is provided with second cleaning means, generally designated by the numeral 30, and comprising at least one paper roll 11. The paper roll has several easily breakable lines for allowing a piece of paper 14 to detach and being brought over the templates 12, by means of a presser 13 movable along two cartesian axes, for removing any ink possibly staining the templates. When the templates have been cleaned, the movable presser 13 unloads the piece of paper in a collector, not illustrated, opposite the roll 11. More particularly, the presser 13, spaced from one of the templates 12, moves to the roll 11. Then the presser 13 lowers toward the roll 11 and drags it, causing the detachment of the piece of paper over the templates and cleaning them. The piece of paper is then unloaded in the collector. The present invention also relates to a screen printing process which is implemented by the above described apparatus. The method for screen printing from one edge to the other of a rigid material consists of arranging a design on a printing frame 3. All the perimetric dimensions of the design are proportionally greater than the dimensions of, for example, the glass pane 6 to be printed across the edges without discontinuity. After the glass pane 6 has been centered on a printing bed 2, the design is printed on the pane by screen printing beyond the edges of the pane 6. Of course, the ink belonging to the area of the design which goes beyond the edges of the glass pane 6, will go over the opposite side of the printing frame and will have to be removed before the successive printing operation. Therefore, after spacing the printing frame from the glass pane 6, ink which has not been deposited on the glass pane 6 because of the lesser dimensions of the pane with respect to the design 5, that ink is scraped off the lower face of the printing frame facing the glass pane 6. In this manner, a screen print has been obtained on all the edges of the glass pane 6 without discontinuity and regardless of any variation of the dimensions of the glass pane with respect to the nominal dimensions. Conveniently, the scraping operation of the lower face of the printing frame 3 is performed when the printing frame is spaced from and parallel to the printing bed 2. After the last scraping operation (return of the scraper or scrapers) a supplementary removal operation is performed for removing any possible ink leftovers by means of absorbent paper, as already described, or equivalent products, without lengthening the printing process. In case the glass pane 6 is retained, as illustrated in Fig. 6, by templates, these templates may be subjected to an automatic cleaning operation of any ink which may have deposited on the templates. This cleaning operation is performed simultaneously with the scraping operation thereby obtaining a screen printing process having the same length of a conventional printing process but with the described advantages. The inventions achieves the intended aims and has important and considerable advantages. It has in fact been devised a new process and apparatus for screen printing from one edge to the other of an object made of rigid material even when the perimetric dimensions of the object have a positive or negative variation with respect to the nominal design dimensions. Furthermore, with the process and apparatus according to the invention it is possible to screen print a rigid object independently from the standard parameters conventionally used in screen printing. The apparatus and process for screen printing according to the invention also allow to reduce the cost of each produced item and the start up costs for modifying the existing production lines. The apparatus and process according to the invention may have numerous modifications and variations, all within the inventive concept. Furthermore, all the details may be substituted with technically equivalent elements. The materials employed, as well as the dimensions, may be any according to the specific needs and the state of the art.

Claims: Apparatus for screen printing from one edge to the other of an object in a rigid material comprising a printing bed (2), a printing frame (3) associated with said printing bed and supporting a design (5) to be printed on said object (6), a means for distributing ink on said printing frame, means for pressing ink through said design and at least a first means (7) for scraping said ink from above said printing frame, characterized in that it comprises second ink scraping means having at least one scraper (8) acting on said lower face of said printing frame facing said object (6) for removing said ink from a portion of said design which exceeds the perimetric dimensions of said object to be printed and means for removing said ink from at least said scraper, said at least one scraper moving along a first path parallel to the path followed by said first scraping means and by said distribution and pressing means and said removing means (20 moving along a second path parallel to the axis of said at least one scraper and orthogonal to said first path. Apparatus, according to claim 1, characterized in that said means for removing said ink comprises at least one roll (20) made of an absorbent material and acting on said at least one scraper by rotating around the axis of said roll and, simultaneously, by moving parallel to the axis of said scraper. Apparatus, according to one or more of the preceding claims, characterized in that said means for removing said ink comprises at least one presser member (23) for pressing said roll, said presser member being supported by a collecting tray (21) for collecting said ink removed from said roll, said tray being movable, at a right angle with respect to said axis of said scraper, by means of moving means (22). Apparatus, according to one or more of the preceding claims, characterized in that said axis of said scraper forms an angle equal or lesser than 90° with the plane of said printing frame, in the direction of advancement of said scraper member. Apparatus, according to one or more of the preceding claims, characterized in that it comprises first cleaning means (24, 25, 26) for cleaning said lower face of said printing frame, said cleaning means comprising a first feed roll (24) for feeding absorbent paper (25) and a second motorized roll (26) for winding said absorbent paper, a pusher (27) being provided between said first roll and said second roll, said pusher being vertically movable with respect to said printing frame, for placing said paper into contact with said lower face of said printing frame. Apparatus, according to claim 5, characterized in that said pusher comprises a plurality of holes (28) on its surface, said holes being adapted to suck air for gripping and guiding said paper. Apparatus, according to one or more of the preceding claims, characterized in that it comprises second cleaning means (30) for cleaning centering templates (12) of said object on said printing bed. Apparatus, according to one or more of the preceding claims, characterized in that said second cleaning means comprises at least one absorbent paper roll (11) having an easily breakable line, and at least one presser (13) movable along two cartesian axes for detaching said a piece of paper (14) from said paper roll, and for moving said paper piece into contact over said centering templates (12) for cleaning said templates, and for discarding said piece after use into a collector opposite said roll. Method for screen printing from one edge to the other of an object made of a rigid material comprising the steps of: arranging a design on a printing frame, all the perimetric dimensions of the design being proportionally greater than the dimensions of said object; centering said object to be printed on a printing bed, printing said design on said object exceeding the printing on at least one of the edges of said object, spacing said printing frame from said printed object, scraping by at least one scraper, from the lower face of said printing frame facing said object, ink which has not been deposited on said object because of the lesser dimensions of said object with respect of said design and removing said ink from at least said scraper along a path parallel to the axis of said scraper. Method, according to claim 9, characterized in that, after said last step of scraping said ink from said lower face, said lower face is subjected to an automatic supplementary removing operation of possible leftovers of said ink. Method, according to claim 9, characterized in that simultaneously to said scraping of said lower face of said printing frame, there is performed an automatic cleaning operation of possible ink staining said centering templates of said object on said printing bed.

Inventors: ROVARIS LORENZO, ROVARIS, LORENZO
Applicants: ASCO SCREEN PROD SRL, ASCO SCREEN PRODUCTS S.R.L.
Application year: 1994
Main classification: B41F15
IPC codes: B41F15, B41F35